Recovery and regeneration of isobutene



July 10, 1945. E. E. wlLLAuER Erm. 2,380,350

RECOVERY AND REGENERATION OF ISOBUTENE Filed July ll, 1942 .pascual-a v8 y Patented July 10, 1945- UNITED STATES c, RECOVERY AND REGENERATIQNAvIsom1`r'1rz1srni Earl E. Willauer, Cranford, andnsley Pilones,

l Baskng. Ridge,'N. J., assignors. to'Standard Oil Development Company,a corporation oi. Del- ,j

awareL y Application 'July 11,1942, serial Nc. 450,524

s claimsi v(c1. aco-471)" The present invention relates to improvementsin the process for theseparation andY recovery of isobutenerfrommixtures of olens and saturated Where''maximumA isobutene recovery is'to be had it is ir'nperativeL that the regeneratable higherboiling`compoundsA be continuously vrecycled to hydrocarbons and moreparticularly to a method c of recovery and regeneration of isobutenefrom'l acid solutions used' "to extract isobutene from ^mixtures ofsaturated'. and unsaturated hydroyoarbons. i y .Y y

There are many'chemieal processes in which it isa decided advantage to.use as ubstantially the regeneration zone.

vWhen steam-stripping normal butenefrom acid extracts,'the.total'recycle stream vcan-be" returned c to the regeneration Vzone, thepolymer being cone pure isoolefln, unmixed with diluents, ksuch ,as

r'saturated hydrocarbons. For example, in chem'- ical reations with thegaseous'isooleiinsin which pressureY is advantageous, V'the effectivepressure is normallyv the partial pressure -of the reactive f Yisoolefln in the mixture; In such cases, substanl V tially pure isoolenspermit much lower-pres-V sures to be employed'and less 'gas to be'comtinuouslyremoved with the spent'acid. However,I in the case ofisobutene regeneration where lower acidities and somewhat lowerregeneration zone temperatures are employed, the polymerformedfjis-chiefly dimer and coldimer and as f vsucl'iI--isi-too Alow-boiling forfremoval with thev spentf'acid resulting in a build-up ofthis material within'` the regeneration zone.

A satisfactory Autilization` of the liquid residue `from thisVfractionation, 'which consists largely of polymerl and valcohol, hasnot'previously been pressed than in the case `of gas mixturesjpo'orinreactive isoolevfins; Also', in many casesy the isooleiin reaction maybelreversible, the propere Y tion of the desired product being dependentupon the concentration of reactive isooleiinin the mix ture. In suchcases, thef dilution of the'isoolen. in the mixturerwith a diluent, suchas a saturated` hydrocarbon, may so affect the yield ofthe de-A c siredreactionproduct as to render' the process' unproiitable. Also, thedesired reaction. product Vmay be very volatile orvtheA chemicalreagent*v used to react with isoolen may be very volatile and carriedaway' `by the relatively unreactive A diluent.V K When paraflinsdehydrogenated. The isooleflns present'doV not Y dehydrogenatebutugradually accumulate and reducethe yields'of the diolens considerably,

therefore, it is necessary to removeltlie'i'soolei'lns from the recyclestock if suitableyields areA totA be obtained. l d Y It isknown in theart that"Y isooleiins mayy be dissolvedV from ahydrocarbon'mixtureby'con#l tacting with sulfuric acid solutions andthat these' isoolens may be recovered by-diluting and! heat- ,Y

` v and olei'lns are dehydrogenatedv to 'form diolens, thefdioleflns areseparated and the residual hydrocarbons recycled to be further"developed and it constitutes a. considerable loss of isobutene.' Byexisting,procedure,iappro1d mately v'G5-'15% lof the isobutene initiallypresentlinr C4 cut are vrecoveredflvvhereasapproximately`25-35%" areconverted to other less desirableliquid products. I Even when theseliquid ,productsv were" redistilled by complicated pro-- Vcedurevinvolving ternary azeotropes the quantity of isobutene recoveredwas-relatively low.y

It is an.` object of` this invention to substantial*- ly iiicre'asetheamounts of isobutenew that are recovered where sulfuric acid is used asthe ab-l sorbent -for the separation of isobutene-'from the saturatedand unsaturated hydrocarbons.

Another object of-this invention is to recover'ath least 90 to' 95%oftheV isobutene in` pure form and substantially reduce the amount ofundelsirable'-products that are produced.l This and "that is present. .IY

ing theacid solution. kIn the processingV of a C4 cut it is establishedvpractice to removethe isoi butene rst by contacting the hydrocarbon mix-Y ture with a sulfuric acid solution of approximately v65% concentrationand v at a temperature of approximately 65 F. The acid extract isdiluted 4 with steam and -heated to removeoverhead a gaseous mixture ofisobutene, polymer, tertiary butyl alcohol, ether, and water. This vapormixture is fractionated for the recovery of isobutene.

other objectsv of thed invention will be more 'clearly understood withreference to the drawing.

A C4 cut containin both 'unsaturated and saturated hydrocarbons iirsttreated with sulfuric acid of? concentrationat'aftemperatureapproximately- 615 F. to remove. isobutene Referring tothe drawing, the C1. cut passed through a pipe I at the bottom ofabsorber 2 where sulfuric acid at 65%-concentration is introducedthrough pipe 3. VThe C4 cut passes in 4countercurrent flow to thensulfuric Vacid andthe I unabsorbed'gases,containing the saturated,together with the unabsorbed unsaturated hydrocarbons are` removed fromAabsorber 2 through piped. The sulfuric acidiwith theisobutene' invsolution is removed from the absorber 2 by means of pipe 5 and passedto scrubber 6 where it passes in countercurrent ow to a mixture ofpolymers,

alcohol and water introduced into scrubber 6 by meansof pipe 1. Atemperature not over about 50 F. is maintained in scrubber 6. Acontinuous acid phase is maintained in scrubber 6. The sulfuric acidwith the isobutene in solution and also the alcohol and Water, isremoved by means of pipe 8 and passed to desorber or regenerating zone 9While the polymer, substantially free of Water and alcohol, is removedfrom scrubber 6- by means of pipe I0. In desorber 9, steam is introducedin the lower part by means of pipe II and passes in countercurrent flowto the sulfuric 'of isobutene with a small proportion of polymer andalcohol and water is removed through pipe I2, passed through partialcondenser I3 into the center portion of the isobutene fractionator I4.The spent acid is removed from desorber 9 by means 'of pipe I5. Thefractionator I4 is provided with a reflux regulator I6 and a totalcondenser IT at the upper part of the fractionator. Substantiallypureisobutene of at least 90% purity is removed from the upper part ofthe fractionator through pipe I8 and the residual liquid consisting ofpolymers, alcohol and Water is recycled from the bottom part of thefractionator through pipe I to scrubber 6. A reboiler I9 is provided atthe bottom of the fractionator to maintain the desired temperature.

The spent acid of 43 to 45% sulfuric acid concentrationremoved by pipe Imay be recycled through line I9 to the scrubber 6 to scrub the lpolymer, alcohol and water introduced into the scrubber by means ofpipe 1. This acid not only serves as an efficient scrubbing agent, butalso reduces the o'len/acid molar ratio within the desorber 9. The spentacid and alcohol dissolved TABLE 1 RECOVERY or ISOBUTENE FROM ACIDEx'rRAc'rs Steam regeneration of acid extracts-polymer scrubbed fromrecycle stream Extract feed:

Olefln to acid ratio-mol G1HB/mol H2804 concentration 65 Operatingvariables:

Stripping steam-lbs/gal. of extract fed Water addition torecycle-lbs./gal. of extract fed therein could be returned to the top oran inter- Olen recovery-wt. per cent:

As gas 94.6 As polymer 3.7 As carbon in spent acid 0.5

Total hydrocarbons accounted for-per cent 98.8 Analysis of regeneratedgas:

Per cent unsaturates l 99.3 Per cent isobutene 1 98.1 Per cent n-butene(by difference) 1.2 Isobutene recoveryper cent 94.6 Isobutenefractionator bottoms stream:

Rate-vol. per cent of extract feed-- 62 Polymer-vol. per cent 7 Spentacid: Y

'Iitratable acidity-Wt. per cent H2SO4 44.5 Carbon content-wt. per cent0.1

We claim:

l. Process of separating and concentrating isobutene which comprises thefollowing steps, absorbing isobutene in a sulfuric acid solution ofabout 65% concentration at a temperature of about 65 F., passing thesulfuric acid with isobutene in solution in countercurrent flow to amixture of polymers,v alcohol and water obtainedin a later stage of theprocess, separatingV the polymers and passing the sulfuric acid withalcohol and isobutene in solution into a regenerating zone, introducingsufli'cient steam to reduce the acid concentration to `43 to 45% andsubjecting the `acid solution to a temperature ranging from 250-325 F.,separating an overhead of isobutene, polymers, alcohol andv water,fractionally distilling such overhead to separate substantially pureisobutene and a residual liquid containing the polymers, alcohol andwater, and recycyiing the residual liquid to contact the sulfuricacid'with the isobutene in solution in countercurrent flow as aforesaid.

2. Process of separating and concentrating isobutene from mixtures ofhydrocarbons containing isobutene comprising treating a mixture ofhydrocarbons containing isobutene and butene with sulfuric acid of about65% concentration at a temperature of about 65 F., separating thesulfuric acid solution, introducing suflicient steam to the sulfuricacid solution to reduce the acid concentration to 43-45% and raise thetemperature of the sulfuric acid solution to to 260 F., wherebypolymers, alcohol land Water are formed, separating an overheaddistillate containing isobutene, polymers, alcohol, and Water,fractionally distilling the overhead distillate to separate isobutenefrom a residual liquid, washing the residual liquid in countercurrentiiow with sulfuric acidof 657% concentration withv isobutene insolution, separating a layer of polymers resulting from said washingoperation, and passing the acid solution to be steam diluted anddistilled.

3. Processk of separating and concentrating isobutene from mixtures ofhydrocarbons containing saturated and unsaturated hydrocarbons whichcomprises extracting the isobutene from a mixtureof hydrocarbonscontaining saturated and unsaturated hydrocarbons by means of sulfuricacid of 65% concentration maintained at a temperature of about 65 F.,steam diluting the acid solution to reduce the acid concentration toi43to 45%, and raising the temperature to 160 F. to 260 F., wherebypolymers,

alcohol andrwater are formed, separating `an overhead distillate,iractionating thev same to separate isobutene from a residual solutioncontaining polymers, alcohol and water. and washing the residualsolution with an acid solution obtained by contacting sulfuric acidoi-65% concentration at a temperature of about 65j' F., with ahydrocarbon mixture of saturated and unsaturated hydrocarbons containinglsobutene, and

separating' aopolymer layer, resulting from said.

washing operation.

, i EARL E. WILLAUER.

INSLEY P. JONES.

